Ram type steering gear is one of the commonly used steering gear construction and is quite expensive in construction. The basic principle is same as that of a hydraulically-driven motor engine or lift.
There are four hydraulic cylinders attached to the two arms of the actuator disc, on both sides. These cylinders are directly coupled to electrically driven hydraulic pumps which generate hydraulic pressure through pipes. This hydraulic pressure field present in the pumps imparts motion to the hydraulic cylinders, which in turn corresponds with the actuator to act upon the rudder stock. As we know, rudder stock is an indispensable part of the entire steering gear arrangement of ships and dictates the exact behaviour of the rudder response.
The sense of turning the rudder is guided by the action of the hydraulic pump. The physics behind its function can be explained better with the help of the following figure.
Here the cylinders denoted A and C are connected to the discharge side of the pump. This generates a positive pressure in the piston cylinders. On the contrary, the other two cylinders B and D are connected to the suction side of the pump. This creates a negative pressure in the cylinders. The resultant forces create a clockwise moment in the rudder. To put it simply, positive and negative pressures from pumps generate lateral forces on the rams which create a couple for turning the rudder stock.
Similarly, to put it in a anticlockwise turning sense, the reverse is carried out, viz. the discharge ends of the pumps are connected to the cylinders B and D, while the suction side of the pumps are to A and C. This reverse pressure flow from hydraulic pumps is achieved with the help of control valves operated from the wheelhouse.
The ram type steering gear arrangement produces a considerably high value of torque for a given applied power. The hydraulic oil pressure varies from 100 bars to 175 bars depending on the size of the rudder and torque required.
Structural features
- Electro-hydraulic driven
- 2 or 4 cylinders
- 1 or 2 rams
- Rudder stock diameters 250 - 500mm
- Working torque 160-1000 kNm
- For 2x 35° or 2x 45° rudder angle
- Hydraulic pumps of fix displacement
- Incorporated electro hydraulic drive and rudder carrier with shaft sealing
- Compact design, no assembly work at Shipyard
- Conical hydraulic shrinkfit connection to rudder stock (keyway on demand)
- Installation on steel chocks
- Fastening by stopper or reamer bolts
- In emergency case easily separation and operation with 2 cylinders (manually, automatically)
